Problem: Simplify to lowest terms. $\dfrac{25}{20}$
What is the greatest common factor (GCD) of 25 and 20? $25 = 5\cdot5$ $20 = 2\cdot2\cdot5$ $\mbox{GCD}(25, 20) = 5$ $\dfrac{25}{20} = \dfrac{5 \cdot 5}{ 4\cdot 5}$ $\hphantom{\dfrac{25}{20}} = \dfrac{5}{4} \cdot \dfrac{5}{5}$ $\hphantom{\dfrac{25}{20}} = \dfrac{5}{4} \cdot 1$ $\hphantom{\dfrac{25}{20}} = \dfrac{5}{4}$